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LIFE102, Weeks 8 & 10

by: Sydney Dingman

LIFE102, Weeks 8 & 10 Life 102

Sydney Dingman
GPA 3.7

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About this Document

This covers weeks 8 and 10 minus Friday before Spring Break.
Attributes of Living Systems
Erik N Arthun
Class Notes
LIFE102, Attributes of Living Systems, Biology
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This 5 page Class Notes was uploaded by Sydney Dingman on Sunday March 27, 2016. The Class Notes belongs to Life 102 at Colorado State University taught by Erik N Arthun in Winter 2016. Since its upload, it has received 30 views. For similar materials see Attributes of Living Systems in Biology at Colorado State University.


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Date Created: 03/27/16
LIFE102 Week 8/10 Notes  Finishing up Chapter 13: o Mitosis and Meiosis  Three events are unique to meiosis, and all three occur in meiosis 1  Synapsis and crossing over in prophase 1: homologous chromosomes physically connect and exchange genetic information  At the metaphase plate, there are paired homologous chromosomes (tetrads), instead of individual replicated chromosomes  At anaphase 1, is homologous chromosomes, instead of sister chromatids, that separate o Why does sexual reproduction exist?  More genetic variation  The genetic variation produced in sexual life cycles contributes to evolution  Asexual reproduction: Offspring are all genetically-identical (no variation)  Sexual reproduction: Offspring are genetically-different (genetic variation)  Advantage of sexual reproduction: Offspring are less vulnerable to environmental change o Origins of Genetic Variation Among Offspring  The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises in each generation  3 mechanisms contribute to genetic variation: o Independent assortment of chromosomes: homologous chromosomes orient randomly and are divided randomly into daughter cells in meiosis 1 o Crossing over: homologous portions of 2 non- sister chromatids trade places; homologous chromosomes pair: synapsis; pieces of DNA are exchanged, producing recombinant chromosomes o Random fertilization: adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg) 3/21/16, Chapter 14: Mendelian Genetics  Encoding Genetic Information o Gene: Stretch of DNA (part of a chromosome) that contains the information to make 1 protein o Genetic Traits: the physical properties of an organism determined by 1 or more genes  Homologous chromosomes o 2 copies of each chromosome  2 copies of each gene  one copy from each parent o Each copy encodes for the same protein, but with possible variations in sequence o Locus: the location of a gene on a chromosome o Alleles: different versions of a gene o Homologous genes: same locus on different chromosomes  Different Alleles for Flower Color in Garden Peas o Gregor Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments o Genes are given to offspring via gametes o Typical experiment: Mendel mated 2 contrasting, true-breeding varieties, a process called hybridization  Hybridization: forcing to make babies o The true-breeding parents are the P generation  Original generation (first combined plants) o The hybrid offspring of the P generation are called the F1 generation  Second generation (first babies) o When F1 individuals self-pollinate or cross-pollinate with other F1 hybrids, the F2 generation is produced 2  Third generation (second babies of first babies)  Mendel’s Experiments o Crossed white- and purple-flowered pea plants: al F1 hybrids were purple o Crossed the F1 hybrids many of the F2 plants had purple flowers but some had white o Mendel discovered a ratio of about 3:1, purple to white flowers, in the F2 generation  Mendel’s Models o Mendel reasoned that only the purple flower factor was affecting flower color in the F1 hybrids o Mendel called the purple flower color a dominant trait and the white flower color a recessive trait o The factor for white flowers was not diluted or destroyed because it reappeared in the F2 generation o Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F2 offspring o Alternative versions of genes account for variates in inherited characters o The gene for flower color in pea plants exist in two versions; now called alleles o If the two alleles at a locus differ, then the dominant one determines the organism’s appearance, and the recessive allele has no noticeable effect on appearance 3/25/16, Chapter 14 cont.  Law of segregation: the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes o An egg or a sperm gets only one of the two alleles that are present in the organism  The possible combinations of sperm and egg can be shown using a Punnett square o A diagram for predicting the results of a genetic cross between individuals of known genetic makeup  Useful Genetic Vocabulary 3 o An organism with two identical alleles for a character is said to be homozygous for the gene controlling that character o An organism that has two different alleles for a gene is said to be heterozygous for the gene controlling that character o Because of the different effects of dominant and recessive alleles, an organism’s traits do not always reveal its genetic composition o Therefore, we distinguish an organism’s phenotype, or physical appearance, and its genotype, or genetic makeup  Mendel’s Laws of Inheritance o Law of segregation: alleles for a specific trait will separate from each other during gamete formation o Law of Independent Assortment: alleles for one trait will segregate independently of alleles for a different trait  Inheritance of 2 genes o On different chromosomes: independent assortment o Far apart on the same chromosome: can be independent o Close together on the same chromosomes: linked  Extending Mendelian Genetics for a Single Gene o Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations  When alleles are not completely dominant or recessive (incomplete dominance)  When a gene has more than 2 alleles (codominance)  Degrees of Dominance o Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical  Ex. The color of the purple and white Mendel’s pea flowers o Incomplete dominance occurs when the phenotype of F1 hybrids is somewhere in between the phenotypes of the two parental varieties  Ex. The color of the red and white of Mendel’s pea flowers o Codominance: most genes exist in populations in more than two allelic forms and would receive a combination of the two  Ex. Blood types, type AB blood 4  Polygenic Inheritance o Quantitative characters are those that vary in the population along a continuum o Quantitative variation usually indicates polygenic inheritance an additive effect of two or more genes on a single phenotype o Skin color in humans is an example of polygenic inheritance  Epistasis o In epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locus  Ex. In Labrador retrievers and many other mammals, coat color depends on two genes o One gene determines the pigment color (Black/Brown) o The other gene (with alleles E for color and e for no color) determines whether the pigment will be deposited in the hair or not  5


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